Primary storage with integrated protection, referred to as PIP storage, reduces storage costs and reduces the time for backup creation and restoration because of its integrated design. A single PIP storage may utilize any type of non-volatile storage medium such as flash memory, PCIe-connected flash memory, solid state device (SSD), magnetic tape, and magneto-optical (MO) storage media to take advantage of different cost performance characteristics of different non-volatile storage medium.
For example, SSDs can deliver about 500× more input/output operations per second (IOPS) than spinning disk but also have 5× the cost. SSDs, as well as other forms of flash memory, have a limited number of write-erase cycles after which a given region of memory cannot be rewritten.
To obtain the best performance, the architecture of a typical PIP storage system uses a tiered infrastructure, including a larger lower cost and lower performance medium such as hard drive disk storage medium (HDD), and a smaller cache/tier layer of a higher cost and higher performance storage medium (SSD). The challenge is to build the tiered infrastructure economically and with high performance. Typically, HDD is used to provide a bottom layer of large capacity disk storage, and SSD is used to provide a middle layer of cache memory, referred to as data cache.
Data cache accelerates performance, including improving the read latency of primary-like application access in Instant Access/Instant Recovery (IA/IR) use cases. Primary-like application access typically refers to frequent access to approximately 20 percent of data and less frequent access to the remaining 80 percent of data.
One technique for improving performance in tiered storage systems is to use pre-fetching, in which blocks of data are read in advance and loaded into the data cache in anticipation of future potential reads of those blocks of data. In storage systems with ample data cache capacity, pre-fetching and loading more data into cache in a high performance cache memory device such as SSD can be beneficial because it can increase efficiency through an increase in the cache hit rate.
But pre-fetching can also be detrimental in tiered storage systems because it can increase disk Input/Output (TO) operations at the lower performance HDD layer. For example, in virtual machines with integrated data protection (VMIDP) or storage appliances with integrated data protection, such as Data Domain Virtual Edition (DDVE)® appliances from EMC® Corporation, pre-fetching data from low spindle count HDDs can potentially cause I/O operation timeouts.